The present invention relates to a new high yield process for producing substantially amorphous propylene-based polymers having high molecular weights. The invention also relates to the novel class of metal complexes used in the above-mentioned process, as well as to the ligands useful as intermediates in the synthesis of said metal complexes.
Metallocene compounds are well-known in the state of the art as catalyst components in olefin polymerization reactions, in association with suitable cocatalysts, such as alumoxanes or aluminum derivatives. For instance, EP 0 129 368 discloses a catalyst system for the polymerization of olefins comprising a bis-cyclopentadienyl coordination complex with a transition metal, wherein the two cyclopentadienyl groups may be linked by a divalent bridging group, such as an ethylene or a dimethylsilandiyl group.
Another class of polymerization catalysts known in the state of the art are the bridged cyclopentadienyl amido catalysts, which usually include monocyclopentadienyl titanium compounds activated by an alumoxane or other suitable cocatalysts (see for instance EP 0 416 815 and EP 0 420 436).
The international patent application WO 98/22486, in the name of the same Applicant, describes bridged and unbridged metallocenes comprising at least a coordinating group containing a six xcfx80 electron central radical, directly coordinating a transition metal atom, to which are associated one or more radicals containing at least one non carbon atom selected from B, N, O, Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb and Te. Said metallocenes are useful as catalyst components for the production of polyethylene and polypropylene.
The international patent application WO 98/37106 describes a polymerization catalyst system comprising a catalytic complex formed by activating a transition metal compound which comprises a group 13, 15 or 16 heterocyclic fused cyclopentadienide ligand and a metal selected from the group consisting of Group 3-9 and 10 metals; said heterocyclic fused cyclopentadienide ligand preferably contains, as endocyclic heteroatoms, one or more B, N, P, O, or S atoms.
The international patent application WO 99/24446, in the name of the same Applicant, describes bridged and unbridged metallocenes comprising at least a heterocyclic cyclopentadienyl group of one of the following formulae: 
wherein one of X or Y is a single bond, the other being O, S, NR or PR, R being hydrogen or an hydrocarbon group; R2, R3 and R4 are hydrogen, halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94OCOR, xe2x80x94SR, xe2x80x94NR2 or xe2x80x94PR2; a is 0-4. These metallocenes may be used as catalyst components in the polymerization of olefins, particularly in the production of homo and copolymers of ethylene.
The international applications WO 98/06727 and WO 98/06728 describe respectively 3-heteroatom and 2-heteroatom substituted cyclopentadienyl-containing metal complexes, useful as catalysts for olefin polymerization; more specifically, these complexes contain a heteroatom-Cp bond, respectively in the 3-position and 2-position of the Cp, and are used for preparing ethylene/1-octene copolymers.
The Applicant has now unexpectedly found a new class of metallocene compounds useful as catalyst components in propylene polymerization, able to produce high molecular weight substantially amorphous propylene (co)polymers in high yields.
An object of the present invention is a process for producing substantially amorphous propylene homopolymers or copolymers comprising contacting propylene, optionally in the presence of one or more olefins selected from the group consisting of ethylene, alpha-olefins of formula CH2xe2x95x90CHRxe2x80x2 wherein Rxe2x80x2 is a linear or branched C2-C10 alkyl or non conjugate diolefins containing up to 20 carbon atoms, under polymerization conditions with a catalyst system comprising:
A) a titanium complex of formula (I): 
wherein: Ti is titanium;
X is a nitrogen or phosphorus atom;
Z is a C, Si or Ge atom; the groups R1, equal to or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals optionally containing Si or heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements, or two R1 groups form together a C4-C7 ring;
Y1 is an atom selected from the group consisting of NR7, oxygen (O), PR7 or sulfur (S), wherein the group R7 is selected from the group consisting of linear or branched, saturated or unsaturated, C1-C20 alkyl, C6-C20 aryl and C7-C20 arylalkyl radical;
the groups R2 and R3, equal to or different from each other, are selected from the group consisting of hydrogen, halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94OCOR, xe2x80x94OSO2CF3, xe2x80x94SR, xe2x80x94NR2 and xe2x80x94PR2, wherein R is a linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl radical; two R can also form a saturated or unsaturated C4-C7 ring, preferably R is methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, phenyl, p-n-butyl-phenyl or benzyl radical, or R2 and R3 form a condensed aromatic or aliphatic C4-C7 ring that can be substituted with one or more R9 groups wherein R9 is selected from the group consisting of halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94OCOR, xe2x80x94OSO2CF3, xe2x80x94SR, xe2x80x94NR2 and xe2x80x94PR2, wherein R has the meaning reported above, or two vicinal R9 groups form together a condensed aromatic or aliphatic C4-C7 ring;
the groups R8, R4 and R5, equal to or different from each other, are selected from the group consisting of hydrogen, halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94OCOR, xe2x80x94OSO2CF3, xe2x80x94SR, xe2x80x94NR2 and xe2x80x94PR2, wherein R has the meaning reported above, or R8 and R4, R4 and R5 or R5 and R8 form together a condensed C4-C7 ring that optionally can be substituted with one or more R groups;
the group R6 is selected from the group consisting of a linear or branched, saturated or unsaturated C1-C20 allyl, C6-C20 aryl and C7-C20 arylalkyl radical, optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements;
the substituents L, equal to or different from each other, are monoanionic sigma ligands selected from the group consisting of hydrogen, halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94OCOR, xe2x80x94OSO2CF3, xe2x80x94SR, xe2x80x94NR2 and xe2x80x94PR2, wherein R has the meaning reported above;
Y2 is selected from the group consisting of CR8 or Y1; and
m is 0 or 1; when the group Y2 is a CR8 group m is l and the 6 membered ring formed is an aromatic benzene ring, when Y2 is different from CR8 m is 0 and the carbon atom bonding the R4 group is directly bonded to the cyclopentadienyl ring and the ring formed is a 5 membered ring; i.e. when m is 1 the compound of formula (I) has the following formula (Ia); 
and when m is 0 the compound of formula (I) has the following formula (Ib); 
wherein L, X, Z, Y1, m, R1, R2, R3, R4, R5, R6 and R8 have the meaning reported above; and
(B) an activating cocatalyst.
The present invention further concerns a titanium complex of formula (I), as reported above, as well as the corresponding ligand of formula (II): 
wherein X, Z, Y1, m, R1, R2, R3, R4, R5, R6 and R8 have the meaning reported above; the above ligands are particularly useful as intermediates in the preparation of the titanium complexes of formula (I), according to the invention.
The titanium complex of formula (I) may be suitably used according to the present invention in a complexed form, for example in the presence of a coordination molecules such as Lewis bases. Preferred complexes of formula (I) are those belonging to the following three classes (1), (2) and (3), having respectively formula (III), (IV) and (V).
Class (1)
Titanium complexes belonging to class (1) have the following formula (III) 
wherein X, Z, Y1, L, R1, R2, R3, R4, R5, R6 and R8 have the meaning reported above with the proviso that R2 and R3 do not form a condensed aromatic or aliphatic C4-C7 ring.
Preferably in the titanium complexes of formula (III):
X is a nitrogen atom; the divalent bridge  greater than ZR12 is preferably selected from the group consisting of dimethylsilyl, diphenylsilyl, diethylsilyl, di-n-propylsilyl, di-isopropylsilyl, di-n-butyl-silyl, di-t-butyl-silyl, di-n-hexylsilyl, ethylmethylsilyl, n-hexylmethylsilyl, cyclopentamethylenesilyl, cyclotetramethylenesilyl, cyclotrimethylenesilyl, methylene, dimethylmethylene and diethylmethylene; even more preferably, it is dimethylsilyl, diphenylsilyl or dimethylmethylene;
Y1 is N-methyl, N-ethyl or N-phenyl;
R2 and R3, equal to or different from each other, are selected from the group consisting of hydrogen, halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94OCOR, xe2x80x94OSO2CF3, xe2x80x94SR, xe2x80x94NR2 and xe2x80x94PR2; more preferably R2 is hydrogen methyl, ethyl, propyl or phenyl; and R3 is hydrogen methyl or phenyl; even more preferably R2 is hydrogen or methyl;
R4 and R8 are hydrogen;
R5 is hydrogen, methoxy or tertbutyl;
R6 is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, phenyl, p-n-butyl-phenyl, benzyl, cyclohexyl and cyclododecyl; more preferably R6 is t-butyl; the substituents L, equal to or different from each other, are preferably halogen atoms, linear or branched, saturated or unsaturated C7-C20 alkylaryl, C1-C6 alkyl groups or OR wherein R is described above; more preferably the substituents L are Cl, CH2C6H5, OCH3 or CH3.
Non limiting examples of complexes of formula (III) are: 
and the corresponding titanium dichloride or dimethoxy complexes.
The titanium complexes belonging to class (1) can be prepared starting from the ligand of formula (IIIa) 
wherein X, Z, Y1, R1, R2, R3, R4, R5, R6 and R8 have the meaning reported above.
Class (2)
Titanium complexes of class (2) have the following formula (IV) 
wherein X, Z, Y1, L, R1, R4, R5, R6, R8, and R9 have the meaning reported above and k ranges from 0 to 4.
Preferably in the titanium complexes of formula (IV):
X is a nitrogen atom; the divalent bridge  greater than ZR12 is selected from the group consisting of dimethylsilyl, diphenylsilyl, diethylsilyl, di-n-propylsilyl, di-isopropylsilyl, di-n-butyl-silyl, di-t-butyl-silyl, di-n-hexylsilyl, ethylmethylsilyl, n-hexylmethylsilyl, cyclopentamethylenesilyl, cyclotetramethylenesilyl, cyclotrimethylenesilyl, methylene, dimethylmethylene and diethylmethylene; even more preferably, it is dimethylsilyl, diphenylsilyl or dimethylmethylene;
Y1 is N-methyl, N-ethyl or N-phenyl;
k is 0 or 1 and R9 is 2-methyl, 2-isopropyl and 2-tert-butyl;
R6 is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, phenyl, p-n-butyl-phenyl, benzyl, cyclohexyl and cyclododecyl; more preferably R6 is t-butyl;
R4, R5 and R8 are hydrogen atoms;
the substituents L, equal to or different from each other, are halogen atoms, linear or branched, saturated or unsaturated C1-C6 alkyl, C7C20 alkylaryl groups or OR wherein R is defined above;
more preferably the substituents L are Cl, CH3, OCH3 or CH2C6H5.
Non limiting examples of titanium complexes of formula (IV), according to the present invention, are the following: 
and the corresponding titanium dimethyl or dimethoxy complexes.
The titanium complexes belonging to class (2) can be prepared starting from the ligand of formula (IVa) 
wherein X, Z, Y1, R1, R4, R5, R6, R8, R9 and k have the meaning reported above.
Class (3)
Titanium complexes belonging to class (3) have the following formula (V): 
wherein X, Z, L, Y1, R1, R2, R3, R4, R5 and R6 have the meaning reported above.
Preferably in the titanium complexes of formula (IV):
X is a nitrogen atom; the divalent bridge  greater than ZR12 is preferably selected from the group consisting of dimethylsilyl, diphenylsilyl, diethylsilyl, di-n-propylsilyl, di-isopropylsilyl, di-n-butyl-silyl, di-t-butyl-silyl, di-n-hexylsilyl, ethylmethylsilyl, n-hexylmethylsilyl, cyclopentamethylenesilyl, cyclotetramethylenesilyl, cyclotrimethylenesilyl, methylene, dimethylmethylene and diethylmethylene; even more preferably, it is dimethylsilyl, diphenylsilyl or dimethylmethylene;
two Y1 are the same group; more preferably they are NR7 or S;
R2 is hydrogen, methyl, ethyl, propyl or phenyl; and R3 is hydrogen or R2 and R3 form a condensed benzene ring that can be substituted with one or more R groups;
R4 is hydrogen and R5 is hydrogen methyl, ethyl, propyl or phenyl or R4 and R5 form a condensed benzene ring that can be substituted with one or more R groups;
R6 is preferably selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, phenyl, p-n-butyl-phenyl, benzyl, cyclohexyl and cyclododecyl; more preferably R6 is t-butyl;
the substituents L, equal to or different from each other, are preferably halogen atoms linear or branched, saturated or unsaturated C7-C20 alkylaryl, C1-C6 alkyl groups or OR; more preferably the substituents L are Cl, CH2C6H5, OCH3 or CH3.
Non limiting examples of complex of formula (IV) are: 
and the corresponding titanium dichloride or dimethoxy complexes.
The titanium complexes belonging to class (3) can be prepared starting from the ligand of formula (Va) 
wherein X, Z, Y1, R1, R2, R3, R4, R5 and R6 have the meaning reported above.
The ligands of formula (II) can be prepared by a process comprising the following steps:
i) reacting a compound of formula (VI): 
xe2x80x83wherein Y1, m, Y2, R2, R3, R4, R5, and R8 have the meaning reported above,
xe2x80x83with at least one equivalent of a base such as hydroxides and hydrides of alkali metals or alkaline-earth metals, metallic sodium and potassium or organolithium compounds such as butyllithium and methyllithium, and then contacting the obtained compound with a compound of formula R12ZY3Y4, wherein R1 and Z have the meaning reported above, Y3 is a halogen atom preferably chlorine and Y4 is an halogen atom preferably chlorine or a group R6XH wherein R6 and X have the meaning reported above and H is hydrogen;
ii) if Y4 is an halogen atom, reacting the obtained product with a compound of formula R6XH2 wherein R6 and X have the meaning reported above and H is hydrogen and recovering the product.
Compound of formula VI can be prepared according to general procedures known in the state of the art, starting from commercially obtainable products or from derivatives which can be prepared by known methods. Synthesis of compounds of formula (VI) can be found for example in WO 99/24446, WO 01/48039, WO 01/48040 and WO 01/47939.
The ligand can be finally purified by general procedures known in the state of the art, such as crystallization or chromatography. All the steps are carried out in an aprotic solvent that can be a polar or apolar solvent. Not limitative examples of aprotic polar solvents which can be used in the above process are tetrahydrofurane, dimethoxyethane, diethylether and dichloromethane. Not limitative examples of apolar solvents suitable for the above process are toluene, pentane, hexane and benzene. The temperature in the various steps is preferably kept between xe2x88x92180xc2x0 C. and 80xc2x0 C., and more preferably between xe2x88x9220xc2x0 C. and 40xc2x0 C.
The titanium complexes of formula (I) can be prepared by first reacting a ligand of formula (II), prepared as described above, with a compound able to form a delocalized dianion, such as hydroxides and hydrides of alkali metals or alkaline-earth metals, metallic sodium and potassium or organolithium compounds such as butylithium, methylithium, on the cyclopentadienyl ring and on the group X, and thereafter with a compound of formula TiLxe2x80x24, wherein the substituents
Lxe2x80x2 are halogen or xe2x80x94OR, wherein R has the meaning reported above. Non limiting examples of compounds of formula TiLxe2x80x24 are titanium tetrachloride and titanium tetramethoxy.
According to a preferred method, a ligand (II) is dissolved in an aprotic polar solvent and at least two equivalents of an organic lithium compound are added. The thus obtained anionic compound is added to a solution of the compound TiLxe2x80x24 in an aprotic solvent. At the end of the reaction, the solid product obtained is separated from the reaction mixture by techniques commonly used in the state of the art. Non limiting examples of aprotic polar solvents suitable for the above reported processes are tetrahydrofurane, dimethoxyethane, diethylether and dichloromethane. Not limiting examples of apolar solvents suitable for the above process are pentane, hexane and toluene. During the whole process, the temperature is preferably kept between xe2x88x92180xc2x0 C. and 80xc2x0 C., and more preferably between xe2x88x9220xc2x0 C. and 40xc2x0 C.
All the above processes are carried out in inert atmosphere such as nitrogen.
Titanium compounds of formula (I) in which at least one L substituent is different from halogen can be conveniently prepared by methods known in the state of the art for example, such compounds may be obtained by reacting the dihalogenated metallocene with alkylmagnesium halides (Grignard reagents) or with lithiumalkyl compounds.
When one or both L substituents are alkyl, the above titanium complexes (I) can be conveniently obtained by reacting directly a ligand of formula (II) with at least one molar equivalent of a compound of formula TiCl4, in the presence of at least 3 molar equivalents of a suitable alkylating agent; said alkylating agent can be an alkaline or alkaline-earth metal, such as dialkyl-lithium, dialkyl-magnesium or a Grignard reagent, as described in WO 99/36427 and WO 00/75151.
An alternative process for preparing titanium complex of formula (I) in which both L substituents are OR groups comprises to prepare the titanium complex of formula (I) in which two L groups are R and then contact the obtained complex with oxygen. The resulting derivative having as L substituents two OR groups shows a better stability than the correspondent R substituted complex and therefore they can be stored for a long time without losing activity.
Suitable activating cocatalyst according to the process of the invention are alumoxanes or compounds able to form an alkyl metallocene cation.
Alumoxane useful as cocatalyst (B) may be linear alumoxanes of the formula (VII): 
wherein R10 is selected from the group consisting of halogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals and y ranges from 0 to 40;
or cyclic alumoxanes of the formula (VIII): 
wherein R10 has the meaning described above and y is an integer ranging from 2 to 40.
The above alumoxanes may be obtained according to procedures known in the state of the art, by reacting water with an organo-aluminum compound of formula AlR103 or Al2R106, with the condition that at least one R10 is not halogen. In this case, the molar ratios of Al/water in the reaction is comprised between 1:1 and 100:1. Particularly suitable are the organometallic aluminum compounds of formula (II) described in EP 0 575 875 and those of formula (II) described in WO 96/02580. Moreover, suitable cocatalysts are those described in WO 99/21899 and in WO 01/21674.
The molar ratio between aluminum and the metal of the titanium complex is comprised between about 10:1 and about 5000:1, and preferably between about 100:1 and about 4000:1.
Examples of alumoxanes suitable as activating cocatalysts in the process of the invention are methylalumoxane (MAO), tetra-isobutyl-alumoxane (TIBAO), tetra-2,4,4-trimethylpentyl-alumoxane (TIOAO) and tetra-2-methyl-pentylalumoxane. Mixtures of different alumoxanes can also be used.
Not limiting examples of aluminum compounds of formula AlR103 or Al2R106 are:
tris(methyl)aluminum, tris(isobutyl)aluminum,
tris(isooctyl)aluminum, bis(isobutyl)aluminum hydride,
methyl-bis(isobutyl)aluminum, dimethyl(isobutyl)aluminum,
tris(isohexyl)aluminum, tris(benzyl)aluminum,
tris(tolyl)aluminum, tris(2,4,4-trimethylpentyl)aluminum,
bis(2,4,4-trimethylpentyl)aluminum hydride, isobutyl-bis(2-phenyl-propyl)aluminum,
diisobutyl-(2-phenyl-propyl)aluminum, isobutyl-bis(2,4,4-trimethyl-pentyl)aluminum,
diisobutyl-(2,4,4-trimethyl-pentyl)aluminum, tris(2,3-dimethyl-hexyl)aluminum,
tris(2,3,3-trimethyl-butyl)aluminum, tris(2,3-dimethyl-butyl)aluminum,
tris(2,3-dimethyl-pentyl)aluminum, tris(2-methyl-3-ethyl-pentyl)aluminum,
tris(2-ethyl-3-methyl-butyl)aluminum, tris(2-ethyl-3-methyl-pentyl)aluminum,
tris(2-isopropyl-3-methyl-butyl)aluminum and tris(2,4-dimethyl-heptyl)aluminum.
Particularly preferred aluminum compounds are trimethylaluminum (TMA), tris(2,4,4-trimethylpentyl) aluminum (TIOA), triisobutylaluminum (TIBA), tris(2,3,3-trimethyl-butyl)aluminum and tris(2,3-dimethyl-butyl)aluminum.
Mixtures of different organometallic aluminum compounds and/or alumoxanes can also be used. In the catalyst system used in the process of the invention, both said titanium complex and said alumoxane can be pre-reacted with an organometallic aluminum compound of formula AlR103 or Al2R106, wherein R10 has the meaning reported above. Pre reaction time can vary from 20 seconds to 1 hour, preferably from 1 minute to 20 minutes.
Further activating cocatalysts suitable as component (B) in the catalysts of the invention are those compounds capable of forming an alkylmetallocene cation; preferably, said compounds have formula Q+Wxe2x88x92, wherein Q+ is a Brxe2x88x85onsted acid capable of donating a proton and of reacting irreversibly with a substituent L of the compound of formula (I), and Wxe2x88x92 is a compatible non-coordinating anion, capable of stabilizing the active catalytic species which result from the reaction of the two compounds, and which is sufficiently labile to be displaceable by an olefinic substrate. Preferably, the Wxe2x88x92 anion comprises one or more boron atoms. More preferably, the anion Wxe2x88x92 is an anion of formula BAr4(xe2x88x92), wherein the Ar substituents, equal to or different from each other, are aryl radicals such as phenyl, pentafluorophenyl, bis(trifluoromethyl)phenyl. Tetrakis-pentafluorophenyl-borate is particularly preferred. Moreover, compounds of formula BAr3 can be conveniently used.
The catalysts system of the present invention can also be supported on an inert carrier (support), by depositing the titanium complex (A), or the reaction product of the titanium complex (A) with the cocatalyst (B), or the cocatalyst (B) and successively the titanium complex (A), on the inert support, such as silica, alumina, magnesium halides, olefin polymers or prepolymers (i.e. polyethylenes, polypropylenes or styrene-divinylbenzene copolymers). The thus obtained supported catalyst system, optionally in the presence of alkylaluminum compounds, either untreated or pre-reacted with water, can be usefully employed in gas-phase polymerization processes. The solid compound so obtained, in combination with further addition of the alkyl aluminum compound as such or prereacted with water, is usefully employed in gas phase polymerization.
The polymerization yield depends on the purity of metallocenes in the catalyst; the metallocene according to the present invention may be used as such or may be previously subjected to purification treatments.
Catalyst components (A) and (B) may be suitably contacted among them before the polymerization. The contact time may be comprised between 1 and 60 minutes, preferably between 5 and 20 minutes. The pre-contact concentrations for the titanium complex (A) are comprised between 0.1 and 10xe2x88x928 mol/l, whereas for the cocatalyst (B) they are comprised between 2 and 10xe2x88x928 mol/l. The precontact is generally carried out in the presence of a hydrocarbon solvent and, optionally, of small amounts of monomer.
The catalysts of the present invention are particularly advantageous in propylene polymerization, wherein they give substantially amorphous propylene polymers with high activities. When in the compounds of formula (I) Y1 is NR7 and preferably the compounds of formula (I) belong to classes (1) and (2), the propylene polymers obtained with the process of the invention have predominantly syndiotactic structure. The syndiotacticity of a polyolefins can be conveniently defined by the percent content of rr triads, as described in L. Resconi et al, Chemical Reviews, 2000, 100, 1253. When in the compounds of formula (I) Y1 is NR7 and preferably the compounds of formula (I) belong to classes (1) and (2), the propylene polymers obtained with the process of the present invention typically have triad contents in the range 60-80%, more preferably 65-75%. Their syndiotacticity is not high enough to produce substantial crystallinity (as measured by DSC), but it is high enough to generate resiliency in the polypropylene.
Being substantially void of crystallinity, their melting enthalpy (xcex94Hf) is preferably lower than about 20 J/g and even more preferably lower than about 10 J/g.
A further interesting use of the catalysts according to the present invention is directed to the preparation of propylene-based copolymers, wherein suitable comonomers are ethylene, alpha-olefins of formula CH2xe2x95x90CHRxe2x80x2 wherein Rxe2x80x2 is a linear or branched, C2-C10 alkyl such as for example 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, non conjugate diolefins containing up to 20 carbon atoms, for examples said diolefins can belong to the formula CH2xe2x95x90CHxe2x80x94(CRxe2x80x32)hxe2x80x94CRxe2x80x32xe2x95x90CRxe2x80x3 wherein Rxe2x80x3 is hydrogen or a linear or branched, C1-C10 alkyl and h ranges from 1 to 15, such as 1,4-hexadiene, 1,5-hexadiene, 2-methyl-1,5-hexadiene, 7-methyl-1,6-octadiene, 1,7-octadiene, and the like or said olefins can be norbornene or its derivatives such as 5-ethylidene-2-norbornene.
The preferred ranges of composition depend on the type of polymer desired, and on the type of polymerization process employed. For example, in the case of amorphous copolymers of propylene with ethylene, such as those described in EP 729984, the content of ethylene ranges from 1 to 35% by moles preferably from 5 to 20% by moles. In the case of ethylene/propylene elastomers the content of propylene ranges from 20 to 80 wt %, preferably from 70 to 30 wt %, while in ethylene/propylene/diene elastomers the content of the diene, which preferably is ethylidenenorbornene or 1,4-hexadiene, range from 0.5 to 5 wt %.
Moreover, the molecular weight of the polymers can be varied by changing the polymerization temperature or the type or the concentration of the catalyst components, or by using molecular weight regulators, such as hydrogen, as well-known in the state of the art. The molecular weight of the propylene-based polymers may be also easily controlled by copolymerizing small amounts of ethylene.
The polymerization process according to the present invention can be carried out in gaseous phase or in liquid phase, optionally in the presence of an inert hydrocarbon solvent either aromatic (such as toluene), or aliphatic (such as propane, hexane, heptane, isobutane and cyclohexane).
The polymerization temperature ranges from about 0xc2x0 C. to about 180xc2x0 C., preferably from 40xc2x0 C. to 120xc2x0 C., more preferably from 60xc2x0 C. to 90xc2x0 C.
The molecular weight distribution can be varied by using mixtures of different metallocenes or by carrying out the polymerization in various steps differing in the polymerization temperature and/or in the concentration of the polymerization monomers.
The following examples are reported for illustrative and not limiting purposes.
GENERAL PROCEDURES AND CHARACTERIZATIONS
All operations were performed under nitrogen by using conventional Schlenk-line techniques. Solvents were purified by degassing with N2 and passing over activated (8 hours, N2 purge, 300xc2x0 C.) Al2O3, and stored under nitrogen. The cocatalyst was a commercial MAO from Witco AG (10% wt solution in toluene).Me2Si(Me4 Cp)(NtBu)TiCl2 was purchased from Witco AG.
1H-NMR
The proton spectra of ligands and metallocenes were obtained using a Bruker DPX 200 spectrometer operating in the Fourier transform mode at room temperature at 200.13 MHz. The samples were dissolved in CDCl3, CD2Cl2, C6D6 or C6D5CD3. As a reference, the residual peak of CHCl3, CHDCl2, C6D5H or C6D5CH3 in the 1H spectra (7.25 ppm, 5.35 ppm, 7.15 and 2.10 ppm respectively) were used. Proton spectra were acquired with a 15xc2x0 pulse and 2 seconds of delay between pulses; 32 transients were stored for each spectrum. All NMR solvents were dried over activated molecular sieves, and kept under nitrogen. Preparation of the samples was carried out under nitrogen using standard inert atmosphere techniques.
13C-NMR
Carbon spectra were obtained using a Bruker DPX-400 spectrometer operating in the Fourier transform mode at 120xc2x0 C. at 100.61 MHz. The samples were dissolved in C2D2Cl4. The peak of the mmmm pentad in the 13C spectra (21.8 ppm) was used as a reference. The carbon spectra were acquired with a 90xc2x0 pulse and 12 seconds of delay between pulses. About 3000 transients were stored for each spectrum. The ethylene content was determined according to M. Kakugo, Y. Naito, K. Mizunuma, T. Miyatake, Macromolecules 1982, 15, 1150. The 1-butene content was determined from the diad distribution, from the Sxcex1xcex1 carbons, as described in J. C. Randall, Macromolecules 1978, 11, 592.
GC-MS
GC-MS analyses were carried out on a HP 5890xe2x80x94series 2 gas chromatograph and a BP 5989B quadrupole mass spectrometer.
VISCOSITY MEASUREMENTS
The intrinsic viscosity (I.V.) was measured in tetrahydronaphtalene (T) at 135xc2x0 C.
The polymer molecular weights were determined from the viscosity values.
DSC ANALYSIS
Melting point and heat of fusion measurements were carried out on a Perkin Elmer DSC 7 instrument by heating the sample from 25xc2x0 C. to 200xc2x0 C. at 10xc2x0 C./min, holding for 2 min at 200xc2x0 C., cooling from 200xc2x0 C. to 25xc2x0 C. at 10xc2x0 C./min, holding for 2 min at 25xc2x0 C., heating from 25xc2x0 C. to 200xc2x0 C. at 10xc2x0 C./min. The reported values are those determined from the second heating scan. Tg values were determined on a DSC30 Mettler instrument equipped with a cooling device, by heating the sample from 25xc2x0 C. to 200xc2x0 C. at 20xc2x0 C./min, holding for 10 min at 200xc2x0 C., cooling from 200xc2x0 C. to xe2x88x92140xc2x0 C., holding for 2 min at xe2x88x92140xc2x0 C., heating from xe2x88x92140xc2x0 C. to 200xc2x0 C. at 20xc2x0 C./min. The reported values are those determined from the second heating scan.